1. Technical Field
The present invention relates to an abnormality detection device for a hydraulic circuit and an abnormality detecting method for a hydraulic circuit.
2. Related Art
In a hydraulic circuit for an automatic transmission (for instance, a continuously variable transmission (CVT)) of a vehicle, the pressure of the oil, discharged from pump driven by the power of an engine, is regulated and the oil with the regulated pressure is supplied. Nowadays, reduction of the load of oil pumps is demanded because of necessity for improvement in the fuel efficiency of vehicles. As a technique of reducing the load of an oil pump, there is a technique which switches between a fully discharged state where oil is discharged through two discharge ports of the oil pump and a partially discharged state where oil is discharged through one of the two discharge ports. As discharged-state switching units, for instance, a spool valve and a solenoid valve to move the spool valve are used.
However, in the case where a switching unit is fixed in a fully discharged state and is not switchable to a partially discharged state, the load of the oil pump increases and the engine power is consumed more than necessary. In order to detect the fixation for instance, Japanese Unexamined Patent Application Publication (JP-A) No. 2014-234909 discloses a fixation determination device for a fluid pressure pump that is switchable between a fully discharged state and a partially discharged state by operating a switching valve with an electromagnetic valve. When the fluid pressure pump is switched to a partially discharged state, in the case where the difference between a fluid pressure (detected value) and a specified value of fluid pressure is greater than or equal to a predetermined value, the fixation determination device determines that at least one of the electromagnetic valve or the switching valve is fixed in a fully discharged state.
The fixation determination in JP-A No. 2014-234909 makes determination in the case where the condition that the number of engine revolutions is greater than or equal to a predetermined number is met. It is preferable to detect a fixation of a switching unit by a simple method without setting a predetermined condition on the number of engine revolutions.